A touch panel is an input device that is provided on a surface of a display and allows the user to input instructions directly on the display. Touch panels are widely used for various purposes to allow the user to directly input instructions via a visual interface on a display.
A resistive touch panel is a type of touch panel that is widely used. A resistive touch panel includes an upper electrode substrate and a lower electrode substrate on which transparent conductive films are formed. The upper and lower electrode substrates are disposed such that the transparent conductive films face each other. When a point on the upper electrode substrate is pressed, the transparent conductive films contact each other at the pressed point and the position of the pressed point is thereby detected.
There are two types of resistive touch panels: a 4-wire touch panel and a 5-wire touch panel. In the 4-wire touch panel, X-axis electrodes are provided on one of the upper and lower electrode substrates and Y-axis electrodes are provided on the other one of the upper and lower electrode substrates. In the 5-wire touch panel, both X-axis electrodes and Y-axis electrodes are provided on the lower electrode substrate, and the upper electrode substrate functions as a probe for detecting a voltage (see, for example, Japanese Laid-Open Patent Publication No. 2004-272722 and Japanese Laid-Open Patent Publication No. 2008-293129).
An exemplary 5-wire touch panel is described below with reference to FIGS. 1 and 2. FIG. 1 is a perspective view of an exemplary 5-wire touch panel 200, and FIG. 2 is a cut-away side view of the 5-wire touch panel 200.
The 5-wire touch panel 200 includes a film 210, a transparent conductive film 230 formed on a surface of the film 210, a glass 220, and a transparent conductive film 240 formed on a surface of the glass 220. The film 210 and the transparent conductive film 230 constitute an upper electrode substrate, and the glass 220 and the transparent conductive 240 constitute a lower electrode substrate. The upper and lower electrode substrates are disposed such that the transparent conductive film 230 and the transparent conductive film 240 face each other via a spacer 250. The 5-wire touch panel 200 is electrically connected via a cable 260 to a host computer (not shown).
As illustrated in FIG. 3A, electrodes 241, 242, 243, and 244 are provided at the corresponding sides of the transparent conductive film 240. A voltage is applied alternately in the X-axis and Y-axis directions via the electrodes 241, 242, 243, and 244. When the transparent film 230 (or the film 210) is pressed at a contact point A, the transparent conductive film 230 and the transparent conductive film 240 contact each other at the contact point A. Then, as illustrated in FIG. 3B, a voltage Va is detected via the transparent conductive film 230, and the X and Y coordinates of the contact point A are detected.
Here, although the 5-wire touch panel 200 described above can detect the position of one contact point each time, it cannot detect the positions of plural contact points at the same time.
Assuming that the transparent conductive film 230 is pressed at contact points A and B at the same time, and the transparent conductive film 230 and the transparent conductive film 240 contact each other at the contact points A and B while a voltage is being applied alternately in the X-axis and Y-axis directions via the electrodes 241, 242, 243, and 244 (see FIG. 4A), the coordinates of a point that is not pressed and located between the contact points A and B are detected. This is because, as illustrated in FIG. 4B, only one voltage Vc is detected via the transparent conductive film 230 even when the transparent conductive film 230 and the transparent conductive film 240 contact each other at the contact points A and B.